1. Field of the Invention
This invention relates generally to patterned perpendicular magnetic recording media, (also called bit-patterned media or BPM), such as disks for use in magnetic recording hard disk drives (HDDs), and more particularly to BPM disks wherein the data bits are stored on elevated magnetic data islands or pillars isolated from one another by recessed trenches.
2. Description of the Related Art
Magnetic recording hard disk drives with patterned magnetic recording media (also called bit-patterned media or BPM) have been proposed to increase data density. In patterned media the magnetic recording layer on the disk is patterned into small isolated data islands arranged in concentric data tracks such that there is a single magnetic domain in each island or “bit”. The single magnetic domain can be a single grain or consist of a few strongly coupled grains that switch magnetic states in concert as a single magnetic volume. This is in contrast to conventional granular media wherein a single “bit” may have multiple weakly coupled magnetic grains separated by grain boundaries. BPM disks may be perpendicular magnetic recording disks, wherein the magnetization directions are perpendicular to or out-of-the-plane of the recording layer.
In one approach for making BPM disks, all of the layers up through and including the magnetic recording layer are deposited as films on the substrate. The disk is then lithographically patterned, such as by nanoimprinting, after which the disk is etched down through the recording layer to form the individual data islands. However, this can lead to degraded magnetic properties of the islands due to damage from the etching and from removal of the resist material after etching.
In another approach for making BPM disks, sometimes called templated growth, the layers up to but not including the magnetic recording layer and its underlayers (called the magnetic stack) are deposited on the substrate. The structure is then lithographically patterned and pre-etched (i.e., before the deposition of the magnetic stack) to form a patterned first seed layer. Then a separate second seed layer is deposited into the etched spaces where there is no first seed layer. The material of the magnetic stack is then deposited on the patterned seed layers, with magnetic material growing on the first seed layer and nonmagnetic material growing on the second seed layer. One example of this approach, as described in US 20100273028 A1 assigned to the same assignee as this application, has ruthenium (Ru) as the first seed layer and oxide spaces as the second seed layer. Magnetic CoPtCr material and nonmagnetic oxide material is then sputter deposited simultaneously, with the CoPtCr growing on the Ru seed layer and the oxide growing on the oxide seed layer. However, this prior art method is limited to templated growth of the data islands and the nonmagnetic spaces between the data islands in the data regions of the disk, and not to the nondata servo regions of the disk.
Like conventional non-patterned or continuous-media disks, BPM disks also have nondata servo regions that are used for read/write head positioning, and to identify the track being written or read. The servo regions in the pre-etched type of BPM disks with elevated spaced-apart data pillars can also patterned to contain elevated nondata servo islands or pillars that are separated by servo trenches. The servo pillars are “servowritten” or pre-magnetized during manufacturing and are not intended to be rewritten during normal operation of the HDD.
The pattern of servo pillars and trenches differs significantly from the uniform periodic pattern of the data pillars and data trenches. There are different sizes and shapes of servo pillar features and the servo trenches are typically much wider than the data trenches. To generate an adequate servo signal the magnetic field above the servo pillar features at the height of the read sensor must be significantly different from the magnetic field above the etched regions. In BPM disks made by etching the magnetic stack, the magnetic material is removed in the etched part of the servo pattern, which results in the desired magnetic contrast at the read head height. However, because of the wide servo trenches as compared to the very narrow data trenches, the prior art templated growth method, which relies on very narrow data trenches to attract the nonmagnetic material, will not result in a servo pattern that can deliver an adequate servo signal. Also, the difference in topography between the data regions and the servo regions can cause a change in the air flow under the slider that supports the read/write head as the slider moves past the data regions and servo regions. This can cause modulations in the slider flying height, and thus magnetic spacing modulations that degrade the performance of the recording system. Thus to create a reliable head-disk interface, expensive extra process steps, such as planarization, may be necessary for BPM disks.
What is needed is a magnetic recording disk with patterned servo regions that can generate an adequate servo signal and that can be fabricated using the advantages of a templated growth method.